Recent discoveries in Functional Glycomics, the systematic study of structure and function of glycans, demonstrate the importance of glycans in many biomedical processes, including protein folding, cell-cell adhesion, signaling, and pathogenesis. Glycan functions in many of these events are fulfilled by their interactions with glycan-binding proteins (GBPs). These may be broadly defined as any protein, e.g. lectins, glycosaminoglycan-binding proteins, and antibodies, which binds to glycan determinants. Without automated glycan sequencing and synthesis capabilities, the major impediment to Functional Glycomics is the general unavailability of glycans with defined structures. The most comprehensive glycan library has been produced by the NIH-funded Consortium for Functional Glycomics, and is largely available as a glycan microarray of ~600 glycans, which represents less than 20% of the total glycan determinants estimated to be contained within the human glycome. Thus, it is obvious that the next major developments in the evolution of Functional Glycomics must expand the number and diversity of available glycan structures. Our guiding hypothesis is that naturally-occurring glycans in human/animal/plant glycomes are recognized by a large repertoire of GBPs, each of which displays specificity in glycan binding and mode of binding. Despite great efforts and progress from synthetic chemists, the current pace of chemo-enzymatic syntheses of glycans lags far behind the explosive interest in glycomics. Current techniques for the isolation and separation of natural glycans are limited by expensive enzymes and harsh chemical conditions. Therefore they are mainly focused on structural analysis requiring relatively small microgram quantities and are not practical for large-scale production of glycan libraries and functional studies. In addition, the aglycon moieties are typically removed, raising questions about functional integrity of the glycans. To directly address these questions, we have developed novel chemistry to implement an innovative reverse synthesis approach to produce large numbers of glycans in significant quantities from glycoconjugates in abundant natural sources. Building upon our success in preliminary studies, we are able to prepare milligram quantities of tagged N- and O-glycans from glycoproteins, and glycans from glycosphingolipids, through simple one- or two-step procedures. We will refine our mild chemical reactions to manipulate the aglycon moieties; i.e., lipid moiety of glycosphingolipids and the peptide chain of glycoproteins. The new chemical methods allow use of large-scale amounts (gram to kilogram) of starting material (tissue/organ) and will provide enough glycans for both detailed structural analyses and functional studies. Success in this project will generate libraries containing many hundreds of complex natural glycans in milligram quantities that are directly biomedically relevant. These libraries will drive studies of glycan interactions important in normal cellular functions and host-pathogen biology.